This invention relates to a system and method for controlling hydraulic flow through a valve. More particularly, the invention is directed to a system and method for controlling hydraulic flow through a valve by monitoring load pressure of the valve.
It is well known to use a valve in a hydraulic circuit of a machine, such as an excavator or a loader, to control a hydraulic flow from a pump to a cylinder, a hydraulic motor, or any other device. When an operator of the machine actuates a valve by, for example, moving a lever, pressurized hydraulic fluid flows from the pump to the device through the valve. The amount of the hydraulic flow to the device can be controlled by changing the displacement of a valve spool located in the valve.
Typically, a valve used to control hydraulic flow is equipped with a valve spool having metering slots that control flow through the valve. The valve may control various types of hydraulic flows, such as a flow from a pump to a cylinder or a cylinder to a reservoir tank. One of the most prevalent hydraulic circuits used to control hydraulic flow to manipulate the device is an open center system. In the open center system, a hydraulic flow to the device decreases as the load pressure increases. Thus, the open center system provides the machine operator with a feel for the load on the cylinder or device.
To achieve this flow-pressure characteristic, the open center system uses a bypass flow path that passes the hydraulic fluid from the pump to the reservoir. When a machine having an open center system is subjected to a certain load, some hydraulic fluid escapes from the pump to the reservoir through the bypass flow path. As the load pressure increases, the bypass flow increases. Since the hydraulic flow in the bypass flow path passes from the pump to the reservoir without doing work, the open center system wastes hydraulic energy, and thus the system may be inefficient.
For some cases, the machine operator may need smooth acceleration of high-inertia or mass loads rather than a feel for the load. In such cases, it may be desirable to provide a hydraulic circuit having flow-pressure characteristics different from the open center system.
In U.S. Pat. No. 5,218,820, a hydraulic flow control system is disclosed for controlling a hydraulic actuator. The hydraulic control system includes a valve, cylinder pressure sensors, and a computer programmed with a model of the hydraulic actuators under different load conditions. Based on signals from the pressure sensors, the computer sends a signal to control the valve. This system, however, does not provide flexibility to change flow-pressure characteristics.
Thus, it is desirable to provide a hydraulic flow control system that is efficient and provides flexibility to accommodate different flow-pressure characteristics of the hydraulic circuit. The present invention is directed to solving one or more of the problems associated with prior art designs.
In one aspect, a method is provided for controlling hydraulic flow through a valve in fluid communication with a pump and a hydraulic actuator. The method includes monitoring load pressure of the valve and selecting a flow limit and a pressure limit of the valve. A flow-pressure relationship in the valve is determined based on the flow limit, the pressure limit, and a desired flow-pressure characteristic. A hydraulic flow rate command is computed based on the determined flow pressure relationship and the monitored load pressure of the valve.
In another aspect, a method provides a plurality of flow-pressure relationships in a valve in fluid communication with a pump and a hydraulic actuator. The method includes selecting a flow limit and a pressure limit of the valve. A first flow-pressure relationship of the plurality of flow-pressure relationships in the valve is determined based on the flow limit, the pressure limit, and a first desired flow-pressure characteristic. A second flow-pressure relationship of the plurality of flow-pressure relationships in the valve is determined based on the flow limit, the pressure limit, and a second desired flow-pressure characteristic different from the first desired flow-pressure characteristic.
In another aspect, a system is provided for controlling hydraulic flow in a valve in fluid communication with a pump and a hydraulic actuator. The valve has an inlet port and an outlet port. The system includes a pressure sensor assembly for monitoring load pressure and a flow controller electrically coupled to the pressure sensor assembly. The controller includes a flow-pressure control unit is configured to determine a flow-pressure relationship in the valve based on a flow limit and a pressure limit of the valve, and a desired flow-pressure characteristic.
In another aspect, a method is provided for controlling movement of a hydraulic actuator. The method includes storing predetermined valve operational characteristics and generating input signals based on movement of an input device. A flow-pressure relationship is simulated based on the input signals and the predetermined valve operational characteristics. A valve command is generated based on the flow-pressure simulation. Movement of the actuator is caused through communication of the valve command with a control valve in fluid communication with the actuator.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.